As a conventional technique of this type, there are known techniques disclosed in Patent Documents 1 to 3 listed below. Especially, in a housing of an EGR valve disclosed in Patent Document 1, a valve shaft is provided through a bearing and driven to reciprocate (stroke movement) by an actuator to open and close a valve element with respect to a valve seat. A seal member is placed between this valve shaft and the housing to prevent leakage of gas, foreign materials or foreign substances, water, etc. toward the actuator through a gap between the valve shaft and the bearing.